Toad loss, climate linked

Global warming basis of amphibian extinction

A series of environmental dominoes beginning with global climate change may explain one of the decade's most perplexing biological mysteries the sharp decline in amphibians according to a new study of toads in Oregon.

A team of researchers studying western toads in the Cascade Range has tied together a series of seemingly unrelated events, warm weather patterns over the South Pacific, decreased rainfall in the Pacific Northwest, ultraviolet radiation and a fungus-like pathogen.

Simply put: The research team found that unusually dry winters caused by El Nieant ponds in which toad embryos mature contained less water, making them more vulnerable to both ultraviolet radiation and a destructive fungus.

"We don't think it's one single answer," said Andrew Blaustein, biology professor at Oregon State University. The research team's conclusions are to be published today in the journal Nature.

The Oregon scientists "have identified, for the first time, a complete chain of events whereby large-scale climate change leads to high mortality in a declining population," said ecologist Alan Pounds at the Golden Toad Laboratory for Conservation in Costa Rica.

The study has implications for other species, by demonstrating the "growing recognition of the connection between climate and epidemics," Pounds said in a commentary accompanying the study. "Climate only loads the dice for disease outbreaks."

The research team led by Joseph Kiesecker, a professor of biology at Penn State University, used data from as far back as 1990 to monitor toad breeding activity at sites 4,000 to 7,000 feet above sea level in lakes and ponds in Oregon's northern Cascades.

The findings suggest how a global phenomenon like climate change may be interacting with local factors to destroy amphibians that have existed on Earth since before the age of dinosaurs. Since 1980, at least 20 amphibian species have become extinct, and many others are shrinking dramatically in regions as distant and different as Oregon and Costa Rica.

"What's coming home is that these environmental fluctuations appear to be sufficiently severe that, when coupled with other factors, they're having a devastating effect on wildlife," said David Wake, a University of California, Berkeley professor of integrative biology and a leader in the study of decreasing amphibian populations.

"This is a new kind of environmental biology," Wake said, "and we're really getting introduced to it in a grim way."

"Our findings support the hypothesis that climate-induced fluctuations in water depth have caused unusually high mortality of embryos by influencing their exposure to UV-B radiation and consequently their vulnerability to (fungal) infections," Kiesecker, Blaustein and coauthor Lisa Belken wrote.

Scientists are still wondering why a fungus that has long coexisted with the western toad may be wreaking havoc today.